You’ve been playing Dungeons and Dragons for a long time. Your players know all of the monster stock abilities to the point where one of the players starts to call out what the monster's next action will be because it’s simply that predictable.
But instead of cleaving it’s weapon into it’s foe, the vile orc inhales sharply and breaths out a cone of fire onto the party. Some of the players may be delighted with surprise, some may scowl, saying that the DM is cheating, but you know better. Right?
Well, just in case you don’t, let us talk about this.
First off, I would like to mention that changing up a monster's special abilities isn’t something that I do very often. I’ll add levels or class to a monster, which in turn will add special abilities, but I won’t generally straight up change abilities they have. Now, I don’t mean to say that it should never be done, it’s just not an option I use very often.
What do I mean by Special Abilities?
While all monsters have an attack routine of some sort, most monsters will have special abilities that go beyond what a normal creature can do.
These abilities range from a merfolk's ability to breath underwater, to a homunculus’ Telepathic Bond, to a hook horror’s Multi attack.
Some abilities are more passive while others are active and can be devastating in combat.
So let’s take a look at our good ol pal, the orc. Regular orcs have a special ability called “Aggressive.” This allows the orc to move towards a hostile creature as a bonus action. This gives the creatures a great gap closing ability in melee skirmishes, making them very tough to escape.
Now, if you have a group of players who are higher level but you still want them to face orcs and still have that feeling of danger, you might consider adding an existing or new special ability to the creatures.
We’ve already spoken about how adding levels and class can do this, and I find those methods are more effective, more complete. But sometimes you just want to add flair to a monster that didn’t previously have it.
Before adding abilities as such, I strongly recommend you come up with a story reason for it. It doesn’t have to be in depth and it doesn’t have to have an impact on your story as a whole. But if you were to give your orcs the ability to breathe fire and have no reason for it, your players may feel cheated, especially if they started to investigate why these orcs could breathe fire.
The flexibility of D&D allows you to grant these powers in a variety of ways.
Let’s say we want to have an entire tribe of orcs who can breathe fire. They would be considered pretty dangerous and would be feared by most other tribes on the area. Rumors of fire breathing orcs may already be in circulation, or it may be something that the players just stumble upon.
How could we grant them this ability in game?
The simplest would be to give them potions of fire breathing. Have them make DEX checks to drink them secretly, if you like. You could even grant them bonuses to do so because they’ve been trained to do this their entire life. They quaff the potion and boom, fire breath. The tribe could have an alchemist that creates them, or maybe there’s a special plant that is easy to process into a fluid that grants the same ability as the alchemical potion. Be as creative as you wish!
Another way would be through magic items, but that can complicate things. Unless you’re planning on having the players fail the encounter, they will almost certainly collect any items they see, including whatever magic item gives them this ability. It also means that an entire orc tribe would be carrying a strong magic item, which means they would have access to a strong magic caster and a lot of money. While this is not impossible it is somewhat improbable.
If you wanted to go this route but don’t want your players can’t use the items, you could curse the items so they don’t work when not in an orc hands. I honestly don’t think magic items are the way to go with something like this because there are too many monsters that would be carrying said item. If this was just for one, or a handful of creatures, magic items can definitely work.
But for a group, something better would be called Blessings or Charms.
In Chapter 7 of the DMG, they speak of blessings and charms, which are in is basic form, special abilities granted to the creature.
Blessings tend to come from Gods or Immortals while charms are often granted by magical items, mystical creatures, etc.
In our above example, a blessing could work if the orcs were devout to a dragon god.
What if they had a powerful shaman who practiced a daily ritual to infuse the orc tribe with this charm that gave them the ability to breath fire 3 times a day?
Charms and Blessings are versatile and have the added bonus of not empowering the players with a ton of magic items while still facing the dangers of said items.
Another method this could be worked is that there is a magic field, again cast by the shamans, that grant the orcs this power. This is why these particular orcs don’t travel very far from home and try to skirmish within the power of the field.
You could decide that anyone in the field is granted the power but doesn’t know it. (The player might realize it after he belches and kills the mage) or you could choose to limit the field to anyone who worships a certain god. (Not a follower of Gruumsh? NO FIRE FOR YOU!)
If you decide to add, modify or remove abilities from monsters, I strongly suggest you have an in game reason for it, as minor as the reason is, so that your players don’t feel you're changing monsters just for the sake of doing so. These changes can make encounters more interesting and again, add some layers of mystery to a monster they may already know really well.
The DMG has a section on creating monsters which can help you decide what you might want to use for your creatures. It’s great even if you are just modifying an existing creature. So make sure to check that out, it’s in Chapter 9.